Medical devices are implanted in human bodies for monitoring physiological conditions, diagnosing diseases, treating diseases, or restoring functions of organs or tissues. Examples of such implantable medical devices include cardiac rhythm management (CRM) devices, neural stimulators, neuromuscular stimulators, drug delivery devices, and biological therapy devices. When an implantable medical device is intended for long-term use in a patient, its size and power consumption are limited by implantability and longevity requirements. Consequently, many implantable medical devices depend on external systems to perform certain functions. Communication between an implantable method device and an external system is performed via telemetry. Examples of specific telemetry functions include programming the implantable medical device to perform certain monitoring or therapeutic tasks, extracting an operational status of the implantable medical device, transmitting real-time physiological data acquired by the implantable medical device, and extracting physiological data acquired by and stored in the implantable medical device.
One type of telemetry between the implantable medical device and the external system is based on inductive coupling between two closely-placed coils using the mutual inductance between these coils. One of the coils is part of the implantable medical device, and the other coil is part of the external system and is typically attached to the patient during a telemetry session. This type of telemetry is referred to as inductive telemetry or near-field telemetry because the coils must be closely situated for obtaining magnetically coupled communication.
Far-field radio-frequency (RF) telemetry provides another means for communication between the implantable medical device and the external system. The far-field RF telemetry is performed using an RF transceiver in the implantable medical device and an RF transceiver in the external system. The far-field RF telemetry frees the patient from any body surface attachment that limits mobility.
The far-field RF telemetry between the implantable medical device and the external system often operates in an environment where various sources of electromagnetic interference exist. For example, a far-filed RF telemetry link operating at a frequency within an unlicensed frequency band may be subjected to environmental interferences from various medical electronic devices, communication devices, and home electronic appliances. Such interferences may interrupt the far-filed RF telemetry link or cause errors in the data transmission.
Therefore, there is a need for ensuring the quality of far-field RF telemetry between an external system and an implanted device when interferences are present.